Ask Slashdot: Best Way To Archive and Access Ancient Emails?

An anonymous reader writes “I started using email in the early 90s and have lost most of that first decade due to ignorance, botched backups, and so on. But since about 2000, I’ve got most — if not all — of my email in some form or other. I run Linux, so this has mainly been in a mix of various programs: Kmail, Evolution, Thunderbird. The past 2-3 years are still on the IMAP servers. My problem is that I only rarely NEED to look back to email of 5 years ago. But sometimes it’s nice. Or I just want to reminisce about something…or find an old attachment that I was sent. But I do not want to be clogging my current email client of choice with vast backups and even more, I don’t know if it will even easily convert. The file structures are different, some are mbox, others maildir, etc., and I would ideally like a way to 1) store and archive these emails, 2) access them, and 3) search by Sender, Subject, Date, Attachments. Is there anything I can do or do I just have to keep legacy applications on hand for this? Should I keep trying to upgrade and pull old files into the new applications? Any help or suggestions about what YOU do would be great.”